1. Field of the Invention
The present invention relates to a process for the stereoselective preparation of vicinal diols by kinetic resolution of functionalized oxiranes using epoxide hydrolases, and an improved process for the preparation of recombinant epoxide hydrolases.
2. Brief Description of the Prior Art
Enantiopure epoxides and the vicinal diols derived therefrom, especially those with further functional groups like carboxylic groups and derivatives thereof are valuable products with biological activity or serve as versatile chiral building blocks for more complex biologically active compounds. Therefore, a great interest exists in the development of methods for the synthesis of such compounds.
P. Hutin and M. Larcheveque (Synthesis 2000, No. 2, p. 220–222) developed a three step synthesis for the preparation of protected 2,3-dihydroxycarbonitriles as a mixture of syn and anti-isomers. This mixture could further be resolved by chromatography. Despite the fact that the enantiomeric purity is satisfying, the procedure has several disadvantages like the need of chiral precursors, an expensive reductant (diisobutyl-aluminiumhydride, DIBALH) and the restriction to carbonitriles as products. Thus it is not suitable for an industrial scale production. Therefore there is still the need for a technically feasible process for the stereoselective preparation of functionalized vicinal diols on an industrial scale.
It is known that some epoxide hydrolases of mammals, plants, insects, bacteria and yeasts are capable of kinetic resolution of racemic epoxides.
Kinetic resolution means that, for example, in an racemic mixture one enantiomer is hydrolized significantly faster than the other, which leads to the formation of enantiomerically enriched vicinal diols and epoxides (the non-converted starting enantiomer) (see also Weijers et al., Appl. Microb. Biotechnol., 1995, 42, 775). But up till now, only unfunctionalized vicinal diols could be obtained via this biochemical route (see for example R.-N. Patel, Stereoselective “synthesis using microbial epoxide hydrolases” in W. Kroutil, K. Faber “Stereoselective biocatalysis”, p. 205–237, Marcel Dekker, New York, 2000.